Page:Popular Science Monthly Volume 60.djvu/305

Rh tube, 64 feet in length, is supported at its middle point by the declination axis, which in its turn is carried by the polar axis, adjusted to accurate parallelism with the axis of the earth. By means of driving mechanism in the upper section of the iron column the whole instrument

is turned about this polar axis at such a rate that it would complete one revolution in twenty-four hours. Although the moving parts weigh over twenty tons the telescope can be directed to any part of the sky by hand, but this operation is much facilitated by the use of electric